Geothermal power

Geothermal power, as Encyclopædia Britannica explains, is a “form of energy conversion in which geothermal energy—namely, steam tapped from underground geothermal reservoirs and geysers—drives turbines to produce electricity. It is considered a form of renewable energy.” The amount of geothermal energy within Earth far exceeds global energy requirements, but harnessing this energy to produce electricity can be difficult. To date, despite its potential, geothermal power makes up less than 1 percent of total U.S. energy use and 1 percent of the world’s electricity generation, which is far less than that produced by most other renewable energy sources. [3] [4] [24]

Use of geothermal energy as a power source is not new. Native Americans used it for cooking some 10,000 years ago, and ancient Greeks and Romans used hot springs to heat their baths. [4]

As Britannica notes,

While humans have long made direct use of geothermal energy as a source of heated water, the first geothermal electric power generation took place in Larderello, Italy, with the development of an experimental plant in 1904. The first commercial use of that technology occurred there in 1913 with the construction of a plant that produced 250 kilowatts (kW). Geothermal power plants were commissioned in New Zealand starting in 1958 and at the Geysers in northern California in 1960. [3]

There are three types of geothermal power plants, according to the U.S. Energy Information Administration:

1. Dry steam plants use steam directly from a geothermal reservoir to turn generator turbines, which produce electricity.
2. Flash steam plants take high-pressure hot water from deep underground and convert it in a “flash tank,” which has a pressure much lower than exists underground, causing some of the water to be “flashed” into steam, which drives generator turbines, producing electricity. When the steam cools, it condenses to water and is injected back into the ground to be used again. Most geothermal power plants are flash steam plants.
3. Binary-cycle power plants transfer the heat from geothermal hot water to another liquid. The heat causes the second liquid to turn to steam, and the steam drives a generator turbine, producing electricity. In this type of plant, the geothermal water never touches the turbine and is returned to the ground. This closed system produces no air emissions. [5]

Because geothermal energy is found mostly at the surface of Earth on major tectonic plate boundaries (where hot springs, geysers, and volcanoes are found), geothermal power plants are generally located near these geologic “hot spots.” Here magma, thin crust, and high-heat flow allow for easy access to underground steam or hot water. This hot material is then used to drive turbines, which produce electricity. The cooled water is then typically returned to the ground via a closed-loop system where the water is circulated in sealed pipes, preventing the contamination of groundwater. [6] [7]

In the United States these hot spots are located in Hawaii and six western states—California, Idaho, Nevada, New Mexico, Oregon, and Utah. The amount of geothermal power generated in these areas varies, from 0.1 percent of a state’s total electricity generation (New Mexico) to 10.1 percent (Nevada). [5] [7]

Globally, 28 countries and territories, including the United States, used geothermal energy from power plants in 2024, according to the International Renewable Energy Agency: Canada, Chile, China, Costa Rica, Croatia, El Salvador, Ethiopia, France, Germany, Guadeloupe, Guatemala, Honduras, Hungary, Iceland, Italy, Indonesia, Japan, Kenya, Mexico, New Zealand, Nicaragua, Papua New Guinea, Philippines, Portugal, Russia, Taiwan, and Turkey (Türkiye). In recent years geothermal energy has also been used by Austria. Although geothermal energy typically accounts for a small portion of a country’s energy portfolio, it accounts for 66 percent of Iceland’s electricity. [8] [9]

Quite a few of those countries, including parts of the United States (i.e., Alaska, California, and the Pacific Northwest), sit along the Ring of Fire, which is a roughly 25,000-mile (40,000-km) ring around the Pacific Ocean that contains over 450 volcanoes; it is the most seismically active area in the world. This is a prime area for geothermal power plants, because these active tectonic plate boundaries produce the necessary high-temperature heat, water, and permeable rock required to generate electricity. [10] [11]

However, as Stanford University geophysicist William Ellsworth notes, though these natural, geographical hot spots for capturing geothermal energy are “an important source of clean energy,” they “are rare and pretty much tapped out.” As a result, there is a need to build geothermal plants in non-seismic, nonvolcanic areas of the world for drilling and reaching deeper geothermal resources. In these areas enhanced geothermal systems (EGSs) are built, where high-pressure fluids are injected into deeply set hot rock to create fissures in places that are insufficiently permeable to water flow; this hydraulic fracturing and high-powered water injection mirrors the methods used in fracking for oil and natural gas. But, instead of mixing water, sand, and chemical additives for this fracturing (as done in fracking), an EGS primarily uses just water for fracturing the hot rock, transporting heat to the surface for generating the electricity. In other words, an EGS is a cleaner form of energy capture compared with fracking, one with less risk of contaminating the surrounding area and groundwater with chemical additives. But an EGS does entail other environmental risks, such as inducing earthquakes because of its high-pressure, deep-drilling techniques. [12] [13]

Geothermal energy can also be generated by smaller heat pumps, which can be installed to service one or several buildings, similar to the way that a small set of solar panels can be installed on the roof of a home or building. As of March 2025, about 1.3 million (1 percent) American homes use a geothermal heat pump. One forecast suggests that as many as 28 million geothermal heat pumps could be installed by 2050, whereas the U.S. Department of Energy says the “technical potential” will exist for 80 million geothermal heat pumps in commercial and residential buildings by that time. [14] [15] [16] [17]

The difference between geothermal large-scale power plants and smaller geothermal heat pumps is in how each harnesses and converts geothermal energy into usable power. Whereas large power plants must convert the energy (converting the high-temperature, deep-underground steam/hot water into electricity), smaller heat pumps circulate fluid (water or a mixture of water and antifreeze) through pipes under the house, building, or adjacent lawn, where they absorb the heat from the constant-temperature ground (approximately 50–60 °F, or 10–16 °C); this heat is then heated or cooled to whatever temperature is desired via a typical HVAC thermostat. Geothermal heat pumps are considered efficient, “direct-use” energy generators because they do not have to convert the energy before it can be used. As Dandelion Energy explains,

Geothermal heat pumps circulate fluid through underground pipes, where they absorb heat. This heat is then extracted, compressed, and circulated throughout the home using its existing ductwork, warming it to whatever temperature you’ve set on your thermostat. This means that heat pumps are much more straightforward solutions for residential heating and cooling: power plants must generate electricity first before they can provide electric heat, but heat pumps can immediately begin circulating heat. [14]

Geothermal power is a highly reliable, renewable, sustainable, and low-emission form of energy, but it can also be expensive, geographically restricted, and environmentally risky, leading to the debate about whether geothermal power is a good form of energy to pursue.

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Discussion questions

1. Is geothermal power a good source of energy? Why or why not?
2. Compare geothermal power with wind and nuclear powers. Which do you think is best?
3. Compare the environmental benefits of geothermal power with its environmental consequences. Which of the two is more significant?
4. What questions do you have after reading the debate above? Where might you find answers?
5. What was the most interesting thing you learned from this debate?
6. Consider how you felt about the issue before reading this article. After reading the pros and cons on this topic, has your thinking changed? How and why?. If your thoughts have not changed, explain how and why you better understand the other side of the debate.
7. Push for the position and policies you support by writing local officials, U.S. senators and representatives, or other people in a position to make the change you champion.